Abstract
This research focuses on the removal of contaminants from wastewaters as a matter of great interest in the field of water pollution. The first decades of the 21st century have brought numerous approaches for the development of cheaper and more effective adsorbents capable of eliminating heavy metals. The study aims to examine the way coffee pulp (Castilla variety from Caldas, Colombia) was used as a bioadsorbent for the removal of Mn (II) from synthetic wastewater to fulfill goals 3 and 6 proposed in the Sustainable Development Goals stated for the 2030 Agenda, particularly in Sections 3.9 and 6.9. In order to achieve this objective, the agricultural residue was subjected to bromatological characterization, determination of the lignocellulosic composition, and identification of characteristic organic functional groups through IR spectrophotometry, using the ATR (attenuated total reflection) technique. Additionally, the optimal parameters for contaminant removal were identified, regarding the biomass quantity, the optimum pH, the stirring time, the adsorption kinetics, the zero charge potential (pHpzc), the adsorption isotherms, and the explanation of the possible adsorption mechanisms between the contaminant, the surface of the coffee pulp, and the capacity of maximum adsorption. The results show that lignocellulosic material presented a cellulose content of 29.93 ± 0.21% and a lignin content of 19.25 ± 0.16%. The optimum parameters found were as follows: Particle size of 180 µm, contact time from 90 min to 100 RPM, optimum pH of 4.0 pH units, room temperature; the kinetic model adjusted to the bioadsorption process was Ho and McKay’s pseudo-second-order, under an isotherm of the Langmuir model, for which the removal presented was 53.40%, with a maximum adsorption capacity of 8.01 mg·g−1. Finally, the novelty of the reported research consists of using coffee pulp as a bioadsorbent without chemical modification, for the removal of heavy metals, in this case Mn (II), in industrial wastewater, which would be another application of this coffee by-product.
Highlights
Water is one of the natural resources that has boosted the development of countries at the economic, social, and environmental levels, in line with the aspects of sustainable development [1]
Manganese (Mn) is a transition metal of atomic number 25, atomic density 7.43 g·cm−3 (20 ◦ C), and atomic mass 54.93 g·mol−1, which is classified as a heavy metal according to the aforementioned characteristics [6]; it can be found in eleven oxidation states ranging from −3 to +7, with the most common colors +2, +4, and +7 [7,8]
The bromatological analysis performed on the Coffee Pulp (CP) determined the humidity, ash, raw fiber, total protein, raw ethereal extract, and carbohydrates, through the analytical techniques reported by the AOAC (Association of Official Analytical Chemistry), while the lignocellulosic content was analyzed according to standards established by ANSI (American National Standards Institute)/ASTM
Summary
Water is one of the natural resources that has boosted the development of countries at the economic, social, and environmental levels, in line with the aspects of sustainable development [1] Due to their advancement, they have used the water resource in domestic and industrial applications where organic, inorganic, and microbiological substances are usually discharged [2,3]. In the treatment for the removal of inorganic pollutants in wastewaters, conventional and non-advanced techniques are used [3], as well as alternative or green technologies The latter are being adopted as sustainable alternatives in wastewater treatment [3,5] and bioadsorption using agricultural by-products has attracted attention as an effective and economic method for metal ions removal, manganese being the one considered as risky for its ecosystem and health repercussions. Manganese (Mn) is a transition metal of atomic number 25, atomic density 7.43 g·cm−3 (20 ◦ C), and atomic mass 54.93 g·mol−1 , which is classified as a heavy metal according to the aforementioned characteristics [6]; it can be found in eleven oxidation states ranging from −3 to +7, with the most common colors +2 (pink), +4 (brown), and +7 (violet) [7,8]
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